Origin: (two heads)
manubrium of sternum
medial portion of clavicle
Insertion: mastoid process of temporal bone
Action:
rotates to side opposite of contraction
laterally flexes to the contracted side
bilaterally flexes the neck

Platysma

Origin: subcutaneous skin over delto-pectoral region
Insertion: invests in the skin widely over the mandible
Action:
depress mandible and lower lip
tenses the skin over the lower neck

Occipitalis (2 bellies)

Origin:
lateral 2/3 of superior nuchal line
external occipital protuberance
Insertion: galea aponeurosis, over the occipital bone
Action: draws back the scalp to raise the eyebrows and wrinkle the brow

Frontalis (2 bellies)

Origin: galea aponeurosis, anterior to the vertex
Insertion: skin above the nose and eyes
Action: draws back the scalp to raise the eyebrows and wrinkle the brow